In certain optical-based automated sorting systems for fruit and vegetables, the product to be sorted is discharged off the end of a horizontal conveyor belt. The product to be sorted is optically scanned while on the conveyor belt and/or while in flight off the end of the belt, and an accept/reject decision is made on the basis of the scan(s). If the product is to be rejected, it will be diverted out of its normal in-flight trajectory, and deflected into a reject chute. If it is to be accepted, it will proceed along its normal in-flight trajectory uninterrupted into an accept chute. This is characteristic of a basic two-way sort operation.
In practice, more complex sort operations are often required. Products may have to be sorted into more than two categories, for example, “Class A”, “Class B” and “Trash”, or alternatively, “Accept”, “Rework” and “Trash”. Originally these more complex sort operations were achieved by passing one of the two streams from a first two-way sort through a second sorter. This required two distinct sorting systems (two optical scanners, two decision making electronics, two rejector devices, two sets of conveying systems etc). In addition to the cost associated with products undergoing two whole sorting operations, this also led to the disadvantage of additional damage to the product.
In the current state of the art as shown in FIG. 1, a single rejector device 101 is used to achieve a three-way sort by having two rejector devices 102, 103 (or two banks of such rejector devices) cascaded one after the other. A single optical scanner and decision making apparatus 104 is used to make the three-way sort decisions. As a product 110 passes the first rejector device 102, an initial sort is made wherein products classified as being of a first category—“Trash” for example—are diverted down a dedicated path 107, remaining products passing on to the second rejector device 103. As a product 110 passes the second rejector device, a second sort is made, wherein products classified as being of a second category (“Class B” for example) are diverted into a second dedicated path 108, leaving the third category of products (“Class A”, for example) to pass on un-diverted to a third path 109.
Instead of needing two complete sorters, the only item that is doubled in quantity is the rejector device. However, there remain some disadvantages with this arrangement. The products must be allowed to fall through a greater height to present them to the two rejector devices in turn. This increases potential for damage to the product. Furthermore, by the time the products reach the second rejector device they have fallen a further distance so that the control and predictability of their precise position is less accurate. This reduces the accuracy of the second sorting operation by increasing the quantity of “missed sorts” (i.e. products that have been selected for diversion but which have actually been missed by the rejector device due to mistiming of the arrival of the product at the rejector device). This also reduces the accuracy of the second sorting operation by increasing the quantity of “accidental sorts” (i.e. products that have not been selected for diversion but which have actually been diverted by the rejector device due to a divert action coinciding with a mistimed arrival of the product at the rejector device). In addition to these problems, while the cost of such a device is lower than that for two complete sorters, there is still a cost associated with having two complete rejector devices. Furthermore, this arrangement is complex and therefore subject to mechanical failure.
U.S. Pat. No. 7,041,926 is directed to a method and system for separating stones of gravel aggregates by one or more predetermined characteristics. This is achieved by passing the gravel aggregate through a drop tube which runs through a plurality of junctions, each of which is connected to three exits: a first distribution hose, a second distribution hose, and a continuation of the drop tube. A pair of independently articulatable diverter devices are situated at each junction, and each pair of diverter devices is cooperatively articulatable such that only one of the three exits at a junction will be open at any given time. While this arrangement allows for complex sorting at a single point, it is still necessary to bear the cost and mechanical complexity of two rejector devices. Furthermore, this arrangement requires coordination of the movement of both independently articulatable diverter devices, adding to the complexity of the overall system.
Accordingly, there is a need for improved methods and systems of automatically sorting into multiple classes.